I don't have an exact date or anything but feeling was with Google in the early 00's. While my "big" first gig was managing Linux and FreeBSD in the data center about the same time, we still had a lot of SGI, IBM/AIX, IBM VM/ESA, AS400, SunOS/Solaris and Windows. Our main driver for getting rid of the big iron was the industry was turning towards cheap commodity systems running Linux and saving the yearly support costs was a big win. Google doing Linux at scale was helpful for the management team to "risk" moving away from tried and true vendors.
The Phalanx defense systems you see on naval vessels.